(1) Field of the Invention
The present invention relates to an optical disk apparatus and a focus jump method for preferably performing a focus jump for a multilayer optical disk having a plurality of recording layers.
(2) Description of the Related Art
In order to increase the capacity of an optical disk, the number of recording layers has been increased. For example, four recording layers are provided in a Blu-ray disk, so that about 100 GB of information can be recorded into one disk. In a multilayer optical disk, in order to accurately move a focus position of a laser light to be irradiated into a desired recording layer, accuracy of a focus jump is required. In general focus control, a current focus position is determined by detecting a reflected light from each recording layer. However, the amplitude of the reflection signal becomes smaller where the recording layer is deeper from the disk surface, and accuracy of a jump tends to be deteriorated as the number of recording layers is increased.
As a focus jump technique in a multilayer disk, the followings have been proposed. Japanese Patent Application Laid-Open No. 2008-34058 describes that the power level of a laser light is increased at the time of performing a focus jump while correcting the aberration of the laser light by aberration correcting means, so that the amplitude of a focus error signal is optimally maintained. Japanese Patent Application Laid-Open No. 2007-26479 describes an optical recording medium in which a recording layer identifying area is provided adjacent to a data area in each recording layer, and the recording layer identifying areas are formed in such a manner that an area with a first reflectivity and an area with a second reflectivity overlap with each other along the direction where the recording layers are laminated.